Chemical ionization ion source

Abstract

A chemical ionization ion source comprising a firt electrode disposed in a discharge region, a counter electrode disposed to confront the first electrode and having at least one space for introducing electrons generated in the discharge region into an ionization region and means for maintaining the counter electrode at a potential higher than that of the first electrode and applying a direct current voltage between the two electrodes, wherein the discharge region and the ionization region are maintained under substantially the same pressures.

What is claimed is: 
     
       1. A chemical ionization ion source comprising a discharge region, an ionization region, a gas inlet and a sampling hole, where electrons generated in said discharge region are irradiated on a gas mixture of reagent gas and sample gas introduced into said ionization region from the gas inlet, said sample gas being ionized by ion-molecule reaction, the resulting ions being emitted from said sampling hole, said chemical ionization ion source being characterized in that said discharge region further comprises (a) at least one first electrode disposed in said discharge region, which is selected from the group consisting of needle electrodes, a knife-edge electrode, a wire electrode and an activated wire electrode having carbon needles grown thereon and (b) a counter electrode disposed to confront the first electrode and having at least one space for introducing electrons generated in the discharge region into said ionization region, wherein said discharge region and ionization region are maintained under substantially the same pressures through at least said counter electrode space. 
     
     
       2. A chemical ionization ion source as set forth in claim 1 wherein ion moving means are disposed to cause ions formed by said ion-molecule reaction to drift to said sampling hole. 
     
     
       3. A chemical ionization ion source as set forth in claim 2 wherein said ion moving means is an electrode which is disposed in the vicinity of said sampling hole of said ionization region and has a hole through which said ions can pass. 
     
     
       4. A chemical ionization ion source as set forth in claim 2 wherein said ion moving means is an electrode disposed on the side opposite said sampling hole of said ionization region. 
     
     
       5. A chemical ionization ion source as set forth in claim 1 wherein the counter electrode is a mesh electrode. 
     
     
       6. A chemical ionization ion source as set forth in claim 1 wherein a plurality of electrodes selected from the group consisting of needle electrodes, a knife-edge electrode and a wire electrode are arranged in series in a longitudinal direction as the first electrode, the counter electrode is an electrode having a slit, said sampling fine hole is a strip-like slit, and the longitudinal direction of said first electrode is identical with the longitudinal direction of the slit of the counter electrode and the longitudinal direction of said sampling fine hole. 
     
     
       7. A chemical ionization ion source as set forth in claim 1, wherein the counter electrode is an electrode having a slit.